Diethyl (2-(tosyloxy)cyclohexyl)phosphonates have been prepared to test the hypothesis that the strongly electron-withdrawing phosphonate group can stabilize the formation of a /3 carbocation through hyperconjugation. Systems were constructed with the 180" dihedral angle between phosphonate and tosyloxy that is optimal for such participation and with the 60" dihedral angle that minimizes it. Reactions were carried out in aqueous mixtures of ethanol, trifluoroethanol, and hexafluoro-2-propanol. The 60" case had the standard profile for bimolecular reaction with solvent (kB),w ith a slower rate that is sensitive to solvent nucleophilicity. The 180" case had the standard profile for a carbocation pathway (kc), with a faster rate that is independent of solvent nucleophilicity and with products that are possible only with a carbocation intermediate. These results suggest that the phosphonate group is capable of stabilizing a carbocation, presumably through hyperconjugation, relative to the expectation based solely on its polar effect.